This invention relates to a circuit breaker, and more particularly to the pivoting contact carrying arms of a circuit breaker.
In general, a circuit breaker opens an electrical circuit by separating the current carrying contacts of the circuit breakers. One way of moving contacts, for the purpose of separation, is to mount the contacts on pivoting arms and provide means for pivoting the arms. This type of arrangement is illustrated in U.S. Pat. No. 4,245,203. While the task of separating contacts using pivoting arms may appear to be relatively straightforward, this is normally not the case since a current path between the contact and the pivoting arm base is required. For example, the current path between the contact and the base for the pivot arm can be completed with a flexible wire. The current path between the contact and the support can also be completed with the pivot joint between the pivot arm and the support.
While flexible wires and pivot joints can be used to complete the current path between the contact and the pivoting arm base, these arrangements have problems. For example, some of the problems with the use of flexible wires, are that flexible wires are subjected to much movement over the life of the circuit breaker and are susceptible to fatigue and other types of failure, and some of the problems with the use of a pivot joint, are that the pivot joint can be subjected to electromagnetic blow apart forces and heating due to contact resistance within the joint.
Turning now to the problem of blow apart forces, FIG. 7 is a schematic representation of the current flow through a contact location. The current is represented by the arrows labeled I. This current (I) can be broken into components, and the arrows marked A represent components of the current (I) flowing toward the contact location, and the arrows marked B represent components of the current (I) flowing away from the contact location. These current components A and B, and their associated magnetic fields, interact to produced forces (blow apart forces) which tend to separate the contacts 1, 2. In a pivot joint, the blow apart forces tend to deflect the pivot joint apart to decrease contact pressures. This deflection can result in increased resistance and heating within the joint. Additionally, the deflection within the joint can cause arcing which in turn causes erosion of the pivot joint.
Accordingly, it would be desirable to provide a contact carrying arm pivot joint adapted to carry a portion of or the whole load current of a circuit breaker, wherein the joint minimizes the adverse effects of blow apart forces at the contact locations within the joint.